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Kennedy/Jenks Consultants samples from 10 shallow borings (two samples from 0.0 to 0.5 feet bgs; eight samples from 0.5 to 1.0 feet bgs; and ten samples each from 1.5 to 2.0 feet and 2.5 to 3.0 feet bgs). Results of the soil analyses are provided in Appendices D and E, for soil and groundwater matrices, respectively. Total lead concentrations in soil samples from this investigation (and prior data) were used to prepare isoconcentration maps with 500 and 1,000 mg/kg contours. The soil volume with total lead concentrations greater than 500 mg/kg was estimated at 2,400 cy. Results of other analyses included detection of soluble lead in 20 of 41 soil samples, all at concentrations below the Title 22 Soluble Threshold Limit Concentration (STLC) of 5.0 mg/I. Other soluble metals (barium, cadmium, copper, mercury and zinc)were also detected at concentrations below their respective STLCs. In the groundwater sample, VOCs and TPHd were not detected, but a TPH hydrocarbon mixture was detected at a concentration of 66 micrograms per liter(Ng/1). Based on all of the analytical results obtained to that date, the document included a workplan for soil excavation and disposal. In April 1995, DTSC required that the soil remediation goal be lowered to 220 mg/kg (Terranext, 1996b). Excavation began in July 1995, and 9,900 cy of soil was transported offsite for disposal. An additional 15,600 cy of soil was stockpiled at the eastern end of the OU-1. Soil test pits were dug to assess the extent of remaining affected soil. Seven of the 12 outermost soil test pits indicated in situ concentrations of lead in soil exceeding the soil cleanup levels of 220 mg/kg total lead and 0.015 mg/I soluble lead using a distilled water leaching agent. Based on these findings, it was concluded that a substantial volume of soil remained to be excavated to meet a 220 mg/kg goal. As a result, Southern Pacific decided to cancel the sale and redevelopment of the property. No further excavation was conducted, but restoration of OU-1 proceeded with Regional Board approval. Stockpiled soil was stabilized by a proprietary process, tested to ensure it met the 1,000 mg/kg TTLC and the 5.0 mg/I STLC for lead, and returned to the excavation. Additional clean fill material was imported and placed on top of the stabilized soil. Following completion of the excavation, stabilization and backfilling, an additional four groundwater monitoring wells were installed within areas of former or residual lead-impacted soil. The six wells (including MW-2, which was now accessible)were monitored quarterly, and reports dated September 1996 through March 1997 did not show dissolved lead in samples from any of the wells, during any quarter(Terranext, 1997) (Appendix E). As a result, monitoring was discontinued and a no further action determination was requested from the Regional Board. Considering these results of past investigations and remedial actions, three general areas of interest (AOIs) have been identified within OU-1 (Figure 2) that warrant further evaluation in the RI: • AOI 1 — Remediated Soils. This area encompasses several smaller isolated areas where remedial soil excavation was conducted until confirmation samples showed residual total lead concentrations were less than the 220 mg/kg remediation goal and soluble extract concentrations were less than 0.015 mg/l. These areas were backfilled with clean imported fill material. • AOI 2— Stabilized Lead. In this area, remedial soil excavation was conducted, but confirmation samples indicated that total lead concentrations of soil remaining in-place may be above the 220 mg/kg remediation goal and/or the soluble extract concentrations Remedial Investigation Work Plan Page 5 Former Tracy Railyard, Tracy, California g:Gs-groupladn ingob105W565777.03_iprt10}reportslwork plan4i 6na11 Adoc